Oil and gas wells can have several strings of casing of differing diameters cemented in the well. Each casing string is usually made up of joints of pipe having threaded ends secured together. A typical casing joint has external threads on its upper and lower ends. A casing collar with internal threads secures the threaded ends together. In larger casing diameters, a casing collar with internal threads may be affixed, such as by welding, to one end of each pipe, the other end having external threads. Normally, the operator relies on the friction of the made-up joint preventing the threaded connectors from loosening while running the string into the well. With larger diameter casing, for example, from 16 inch to 36 inch, the friction of the made-up connector may be inadequate to prevent loosening while running the casing.
Operators have employed anti-rotation keys to prevent loosening. In one type, a rectangular pocket or slot is machined on the outer surface of the pin connector. The box connector is machined to include tabs that accept the anti-rotation key. The box connector tab and pin connector pocket will line up after making up the connectors. The workers will then drive a key through the box connector tab and into the pin connector pocket. The key has a slightly greater thickness than the distance from the box connector tab to the innermost wall of the pin connector pocket, resulting in an interference fit. The workers typically will drive the key into place with a hammer.
When the casing is under load, with some designs, the key can loosen. Some designs require specialty tools to install the locking mechanism. Some designs require explosive powered guns to set the locking mechanism. Other designs can be difficult to unlock in the event it is necessary to unscrew the pipe connection. Another design requires drilling a hole for the locking member after the pipe connection is made up. Drilling can result in metal shavings falling down the pipe string, which can cause issues. Further, drilling a made up pipe connection requires a complex drill. If disconnected, then reconnected, it may be necessary to drill another hole, and that hole may overlap the previously drilled hole, limiting the locking capacity.